1. Field of the Invention
Aspects of the present invention relate to a cognitive radio (CR) system. More particularly, aspects of the invention relate to a communication method and apparatus for a distributed network system where CR technology is used.
2. Description of the Related Art
Due to the rapid development of wireless communication technologies, wireless communication systems are currently required to obtain and maintain their own frequency band to overcome disadvantages of coexistence of systems. However, frequency resources for new wireless communication systems are virtually exhausted, since most frequency bands currently available are already assigned according to government policy. Frequency bands are almost all in use, and thus there are no additional frequency bands that may be used.
Cognitive radio (CR) technology is one of the technologies currently being discussed to overcome radio resource shortages. In CR technology, radio resources with a low utilization ratio are identified and frequency radio resources are shared without interfering with systems currently using assigned frequencies. Accordingly, radio resource efficiencies are theoretically expected to improve.
Economic efficiency is one of the advantages of CR technologies. Compared to existing wireless communication services, CR technologies are relatively low priced as wireless frequency bands are used at no charge. CR technologies are also related to the management and distribution of wireless channels with respect to multi-channels and to interference detection technologies that can be used together with next generation wireless communication. For example, CR technologies may efficiently transmit high speed data in dead zones without generating interference. The dead zones are created in cellular environments or rural areas required to improve cell sizes. However, CR technology is in an early stage of the standardization and development process. Accordingly, most technological details of the CR technology has not been determined yet; thus, there are disadvantages to overcome.
To apply communication systems using the CR technology to distributed network environments, each node needs to know whether frequencies are used by an authorized communication provider. Distributed network environments include a mobile ad hoc network (MANET), a wireless local area network (WLAN), and the like. The MANET is a network where mobile terminals can communicate with each other without a fixed infrastructure and is referred to as an infrastructureless network. Unauthorized nodes using the CR technology should use another channel when the nodes determine that an authorized communication provider is currently using the channel. Conventional communication systems are strictly controlled by governments, and thus disadvantages within a given frequency band are considered. However, wireless communication systems using the CR technology avoid incumbent users, that is, authorized communication systems, and sense available channels. Accordingly, a technology that can efficiently report incumbent users with the CR technology is needed.
FIG. 1 is a diagram illustrating an example of a communication environment of a general distributed network system. For example, a MANET is described as the distributed network system. A narrow circle or a circular line around an incumbent user indicates an incumbent system interference area of the incumbent user.
A source node refers to a communication device including data that is transmitted via a wireless interface based on the CR technology. A destination node refers to a communication device that finally receives the data via the wireless interface based on the CR technology. A neighbor node refers to a communication device located at a distance of a single hop from the source node and the destination node. A channel status table (CST) refers to a set of data indicating the status of each channel. The incumbent user refers to a wireless communication system having a legal right to use a frequency. A node using a particular channel using the CR technology needs to change a channel when an incumbent user is using the same channel as the node. A term such as an incumbent system or a user/terminal of the incumbent system may be used instead of incumbent user.
As illustrated in FIG. 1, in the MANET, various unauthorized nodes 100, 101, 102, 110, 111, and 112 can exist in a single space. When packet data is transmitted from a source node 110, i.e., a start point (S), to a destination node (D) 100 via a sub-channel 1 (SC1) in operation S120, the neighbor nodes 101, 102, 111, and 112 can overhear the transmission of the packet data. This overhearing is referred to as listening. When the incumbent user uses a channel 1 (SC1) 150, a channel 2 (SC2) 151, a channel 3 (SC3) 152, and a channel (SC4) 153, respectively, an incumbent user 141 using the SC1 suffers serious interference due to the data transmission of the unauthorized nodes 100 and 110. The unauthorized node 112 sensing a signal of the incumbent user 141 cannot provide information about the interference to the source node 110. Accordingly, the unauthorized node 112 can interfere with the incumbent user 141.
A communication range of an incumbent user 140 using the SC3 reaches the destination node 100. The destination node 100 therefore does not use the SC3 as a data channel, since the destination node 100 recognizes that the SC3 is being used. However, communication ranges of the incumbent users 141, 142, 143, 144, and 145 using the SC1, the SC2, and the SC4 do not reach the source node 110 or the destination node 100. Accordingly, a node transmitting random data cannot ascertain whether the SC3 is being used by an incumbent user. Thus, when the node selects and uses any one of the SC1, the SC2, and the SC4 as the data channel, the incumbent users can be adversely affected by, for example, an interference phenomenon. This problem is referred to as a problem of a hidden incumbent system.
Specifically, a communication method and apparatus of the distributed network system where the CR technology is used in the conventional art has several disadvantages. First, nodes using a same frequency exist in the distributed network system where the CR technology is used, since the disadvantage of the hidden incumbent system cannot be overcome. Accordingly, communication interference deteriorates and a high quality communication may not be guaranteed. Second, the CST cannot be actively updated in the distributed network system where the CR technology is used. Accordingly, an available channel can not be rapidly retrieved.
Thus, a new communication method and apparatus for a distributed network system where CR technology is used is needed.